For the purpose of molding the rigid polyurethane foam, the urethane raw liquid is supplied to a lower mold portion of a mold including upper and lower mold portions so as to produce the foam by clamping the mold. The mold is then opened to release the molded product after curing.
Generally, the mold for foam molding structured to push up the molded product with an ejector pin provided in the lower mold portion for the mold release has been well known. However, the mark resulting from pushing of the ejector pin is likely to be left on the molded product.
Japanese Unexamined Patent Application Publication No. 9-234748 discloses the efficient mold release method without using the aforementioned ejector pin. Specifically, in the disclosed foam molding method, the film is applied along the cavity surface of the lower mold portion, air is fed between the film and the cavity surface to release the film from the cavity surface upon the mold release after the mold opening, and the molded product is extruded outside the lower mold portion by the film.
FIGS. 6a, 6b and 6c are sectional views each showing the generally employed method and the mold used therein as disclosed in the aforementioned publication. The mold is formed of an upper mold portion 2 and a lower mold portion 3 which may be joined and separated. A cavity 4 is formed in the lower mold portion 3.
A polypropylene film 6 which is preliminarily formed to be either similar or identical to the cavity 4 through vacuum forming process is applied to the lower mold portion 3. The film 6 is held on the upper end surface of the lower mold portion 3 with fixation pins 7 and interposed between packings 9 for film air seal disposed on the upper end surface of the lower mold portion 3 and film holders 8 so as to be strongly fixed onto the lower mold portion 3.
A box-like air chamber 10 is formed below the bottom of the lower mold portion 3, to which one end of an air pipe 12 provided with a pressure regulating valve 11 is connected. The other end of the air pipe 12 is connected to an air introduction/suction unit 13, for example, a vacuum pump. The air chamber 10 is communicated with the cavity 4 of the lower mold portion via a plurality of air communication holes (air holes) 14.
In the case where the rigid polyurethane foam molded product is produced using the mold 1, a predetermined amount of the raw material of the rigid polyurethane foam is introduced to the vacuum molded polypropylene film 6 within the cavity 4, and the mold is clamped by joining the upper mold portion 2 with the lower mold portion 3. After the foaming and expansion as shown in FIG. 6a, the upper mold portion 2 is separated to open the mold, and the air introduction/suction unit 13 is activated as shown in FIG. 6b to feed air to a gap 15 between the film 6 and the cavity 4 via the air pipe 12, the air chamber 10 and the air communication holes 14 to push up a molded product 16 together with the film 6. The molded product 16, thus, may be taken out.
Thereafter, air is sucked by the air introduction/suction unit 13 to bring the film 6 into tight fit with the cavity surface, and the process proceeds to the subsequent molding cycle.
In another method for the efficient mold release without using the ejector pin, the air feed means including the valve box and the valve element disposed therein so as to be movable up and down may be provided in the bottom surface of the lower mold portion. Upon the mold release after opening the mold, air is fed to the air feed means to cause the valve element to protrude into the cavity such that the molded product is extruded outside the lower mold portion.
FIGS. 7a and 7b are sectional views each representing the aforementioned method and the mold used therein. FIGS. 8a and 8b are sectional views each representing the air feed means.
The mold 20 is formed of an upper mold portion 21 and a lower mold portion 22.
The lower mold portion 22 includes a cavity 24, and air feed means 23 is disposed in the bottom surface of the lower mold portion 22. The air feed means 23 includes a valve box 25 attached to an opening of the bottom surface of the lower mold portion 22, a valve element 26 disposed within the valve box 25 so as to be movable up and down, and an air tube 25a having one end connected to the lower end of the valve box 25, and the other end connected to an oxygen tank. The valve element 26 is an inverted tapered mushroom valve having a flat top surface. A flange 26a is provided at the lower end of the valve element 26.
The valve box 25 as a cylindrical vessel has an open top surface and a closed bottom surface. Two upper and lower protrusions 27 and 28 are formed on the inner peripheral surface, which interpose the flange 26a. 
Coil springs 30 each serving as an urging member are disposed between the upper protrusions 27 and the flange portion 26a in the urged state. The valve element 26 is urged downward by the coil springs 30. The valve element 26 is closed in the state where the flange portion 26a is pushed against the protrusions 28. At this time, the top surface of the valve element 26 is flush with the bottom surface of the lower mold portion 22. The upper end surface of the valve box 25 is also flush with the bottom surface of the lower mold portion 22. The air tube 25a is attached to the lower portion of the valve box 25.
The molding process to produce the molded product using the mold 20 will be described hereinafter.
In the state where the valve element 26 is closed as shown in FIG. 8a, a mold release agent is applied to the inner surface of the mold 20. Then the raw liquid, for example, urethane and the like is supplied into the lower mold portion 22, and the mold is clamped by moving the upper mold portion to produce the foam as shown in FIG. 7a. Upon completion of curing, the upper mold portion is separated to open the mold as shown in FIG. 7b to allow air to be fed into the valve box 25 such that a molded product 31 is pushed up by the air pressure to be released from the mold.
When air is fed into the valve box 25 through the air tube 25a, the valve element 26 is pushed up by the air pressure against the urging force of the coil springs 30 as shown in FIG. 8b. Air is fed into the space between the bottom surface of the lower mold portion 22 and the molded product 31 from the valve box 25 to push up the molded product 31 to be released from the lower mold portion 22.
When the air feed to the valve box 25 is stopped after the mold release, the valve element 26 is pushed down under the urging force of the coil springs 30 to return to the original state as shown in FIG. 8a. The molding process proceeds to the next cycle.
In the method for releasing the molded product from the cavity of the lower mold portion by the air pressure, if the molded product 31 has a large thickness as shown in FIGS. 7a and 7b, the molded product 31 is pushed up sufficiently by the air pressure. The resultant floating height L of the molded product floating from the upper surface of the lower mold portion 22 is sufficiently large. The operator is allowed to grip the portion of the molded product 31 floating from the lower mold portion 22 so as to easily take the molded product 31 from the lower mold portion 22.
Referring to FIGS. 9a and 9b, if the depth of the cavity 24A formed in the lower mold portion 22A of the mold 20A is substantially small, and accordingly, the molded product 31A has a small thickness, the air pressure is likely to leak from the lower side of the molded product 31A. Accordingly, the resultant floating height L of the molded product 31A is likely to become small. The operator has difficulty in gripping the floating portion of the molded product 31A to be released from the mold.